FIG. 1 is an illustration of a conventional nuclear reactor fuel assembly 10 typically used in commercial nuclear power reactors for electricity generation throughout the world. Several fuel assemblies 10 are placed in a reactor in close proximity to sustain a nuclear chain reaction. A fluid moderator and/or coolant conventionally passes through fuel assembly 10 in a length-wise (axial) direction, enhancing the chain reaction and/or transporting heat away from the assembly 10.
As shown in FIG. 1, fuel assembly 10 includes multiple fuel rods 14 containing fissile material and extending in the axial direction within the assembly 10. Although not shown in FIG. 1, fuel rods 14 are often seated into a lower tie plate 16 and extend upward into an upper tie plate 17 at ends of fuel assembly 10. Fuel rods 14 are bounded by a channel 12 that forms an exterior of the assembly 10, maintaining fluid flow within assembly 10 throughout the axial length of assembly 10. Conventional fuel assembly 10 also includes one or more conventional fuel spacers 18 at various axial positions. Fuel spacer 18 permits fuel rods 14 to pass through grid openings in spacer 18, thereby aligning and spacing fuel rods 14. One or more water rods 19 may also be present to provide a desired level of moderator or coolant through-flow to assembly 12.
FIG. 2 is an illustration of a related art fuel spacer 18 from an axial direction. As shown in FIG. 2, conventional spacer 18 includes several grid openings 41, which may be formed by several ferrules 40. Each ferrule 40 conventionally forms a full circle and is joined with other ferrules 40 to form a grid-like pattern of openings 41 where fuel rods 14 (FIG. 1) should pass and be stabilized through spacer 18. That is, several fuel rods 14 (FIG. 1) may pass through spacer 18 through corresponding ferrules 40 and grid openings 41, when used in an assembly. Ferrules 40 may be joined together by welding among each touching ferrule 40, with perimeter ferrules 40 being welded to perimeter band 49. In this way, each ferrule 40 is rigidly joined to and stabilized with several adjacent ferrules.
Ferrules 40 and thus grid openings 41 may be sized substantially similar to perimeter sizes of fuel rods intended to pass therethrough, permitting a frictional sliding relationship between spacer 18 and a fuel rod. Ferrules 40 in FIG. 2 may further each include two rod-contact stops 42 and one rod-contact spring 43 to control frictional forces when a fuel rod passes therethrough. Grid openings 41 may all be of a substantially similar size and positioned in rectilinear fashion as shown in FIG. 2, or may be positioned and sized differently to accommodate other fuel designs. For example, grid openings 41 for water rods 16 may be larger than grid openings 41 for smaller fuel rods 14. Alternatively, all grid openings 41 may be a same size. Perimeter band 49 may enclose spacer 18 and contact channel 12 (FIG. 1).